Taste and odor have long been associated with the aesthetic suitability of drinking water, although many tastes and odors are not known to be harmful. Some people today will reject potable water simply because it smells or tastes bad. Two of the primary natural causes of disagreeable flavors and odors in surface waters are 2-methylisoborneol (MIB) and geosmin, which are musty-smelling, organic chemicals that are produced by microorganisms. Both compounds can cause detectable tastes and odors in water at concentrations as low as 7 to 15 parts per trillion. Also, MIB and geosmin have been linked to taste-and-odor episodes around the world, and are therefore a global concern. Consequently, effective treatment technologies for controlling MIB- and geosmin-related tastes and odors have garnered much attention.
Numerous studies of treatment techniques for taste-and-odor control have established that activated carbon adsorption is an effective method for removing MIB and geosmin from water. However, activated carbon has a finite capacity for adsorbing organic compounds, and this capacity is generally diminished when the target compound(s) compete(s) for adsorption sites with the natural organic matter found in water. There are significant costs and operational challenges associated with discarding and replacing activated carbon that has become exhausted in its capacity to adsorb organic compounds. Hence there is a need to increase the service life of activated carbon for taste-and-odor removal.
The present invention described herein encompasses several techniques for producing tailored activated carbons with much longer service lives for removing MIB and (by inference) geosmin than current commercial activated carbon products.
The present inventors have discovered that heating an activated carbon in certain gas environments caused favorable changes in the carbon's pore size distribution and surface characteristics. As demonstrated hereafter, the present inventors discovered that taste-and-odor removal, as measured by MIB breakthrough performance, was closely correlated with the carbon properties affected by these heat treatments.
As a broader application, activated carbon is also commonly used to remove a variety of naturally occurring and synthetic organic compounds from water. The present invention described herein could impact all of these activated carbon applications.
The present invention also provides many additional advantages that shall become apparent as described below.